The present invention relates to field sensitive optical displays, particularly of the field effect and field excited types, and to the generation of the fields for activating the displays and to the scanning of the displays. More particularly, the present invention relates to liquid crystal, optoceramic and electroluminescence displays, and electrode and scanning arrangements therefor.
The present invention contemplates utilization of liquid crystal materials in which the propagation or characteristics of light incidence thereon can be altered by inducing an electric or magnetic field in the liquid crystal material. Such liquid crystal materials include, but are not limited to, nematic liquid crystal materials possessing dynamic or quiescent scattering, or twisted field-effect electro-optical properties, and the mixtures of those nematic liquid crystal materials with cholesteric liquid crystal materials.
In a dynamic scattering liquid crystal material, light is transmitted substantially unaffected through the material in the absence of a field. When a field of sufficient magnitude is induced in the liquid crystal material, light incident upon the material is optically scattered and transmission of light through the material is substantially prevented.
A quiescent scattering liquid crystal material possesses field effect electro-optical properties which are the converse of those of the dynamic scattering liquid crystal, that is, in the absence of a field, the quiescent scattering liquid crystal material scatters incident light, while a field induced in the quiescent liquid crystal material causes it to transmit incident light therethrough.
In a twisted nematic liquid crystal material, layers of molecules at opposed surfaces of the material can be caused to be aligned at an angle with each other in the absence of a field. The molecules between the opposed surfaces have varying angular alignments with the result that the molecular orientation through the material from one surface to the other is helical or "twisted." The plane of polarization of plane polarized light is rotated by the angle formed by the opposed surface molecules as the light passes through the liquid crystal material in the absence of a field. The application of a field to the material destroys the twisted alignment of the molecules with the result that the material transmits incident plane polarized light therethrough without substantial rotation of the plane of polarization.
Mixtures of nematic and cholesteric liquid crystal materials provide a storage characteristic to the scattering nematic liquid crystal materials. Such mixtures retain field-induced electro-optical characteristics after the field is removed. The application of an appropriate ac (alternating current) field returns the material to the state it normally possesses in the absence of a field.
Liquid crystal materials of the types referred to, as well as others, are well known in the prior art. See, for example, G. Heilmeier, "Liquid-Crystal Display Device," Scientific American, April, 1970, pp. 100-106; G. Heilmeier, L. Zanoni & L. Barton, "Dynamic Scattering: A New Electrooptic Effect in Certain Classes of Nematic Liquid Crystals," Proceedings of the IEEE, Vol. 56, No. 7, July 1968, pp. 1162-1171; and U.S. Pat. No. 3,918,796 on Nov. 11, 1975 to Fergason.
Nemati scattering liquid crystal electro-optical elements are well known in the prior art, as described, for example, in U.S. Pat. No 3,322,485, issued on May 30, 1967, to Williams. Twisted liquid crystal electro-optical elements which require the use of polarizing elements, are also well known in the prior art, as described, for example, in the aforementioned '796 Fergason patent. The Fergason '796 patent and U.S. Pat. No. 3,834,792, issued on Sept. 10, 1976, to Janning, describe two arrangements for aligning liquid crystal molecules in a display in order that polarized light passing through the material in the absence of a field is rotated. The Fergason '796 patent teaches rubbing each of the glass plates which enclose the liquid crystal material in a single predetermined direction and thereafter positioning the plates with the directions of rubbing of the plates forming an angle through which the polarized light is to be rotated. The Janning '792 patent teaches the growth of an alignment film on each plate and then the arranging of the plates with the directions of growth on each of the plates forming a desired angle with respect to one another. Both the Fergason '796 and the Janning '792 patents disclose arrangements of polarizers and twisted liquid crystal cells.
U.S. Pat. No. 3,820,875, issued on June 28, 1974, to William Bohmer, one of the applicants hereof, discloses devices utilizing field-effect scattering dielectrics, such as for example, nematic liquid crystal materials and mixtures of cholesteric and nematic liquid crystal materials. The '875 patent also discloses scanning devices incorporating such dielectrics. The disclosure of the '875 patent is incorporated herein by reference. The '875 patent also discloses display cells having both a a voltage gradiant can be generated and a conductive electrode. By applying suitable control voltages to such cells and combination of such cells, displays can be formed which include those having a movable dot or line. Sequential scanning of such cells can provide displays comprising patterns or images.
U.S. Pat. No. 3,675,988, issued on July 11, 1972, to Soref discloses liquid crystal display devices in which a variety of images, such as a moving bright spot, a variable length bar, a moving arrow and a moving window, can be generated. The Soref '988 patent discloses a liquid crystal display device which includes transparent electrodes uniformly coated on the surface of opposed plates enclosing the liquid crystal material. One of the electrodes has high resistivity with the result that a voltage gradiant can be generated along the extent of the electrode, i.e., each line location of the electrode will have a different voltage level.
U.S. Pat. No. 3,807,831 issued on Apr. 30, 1974 to Soref discloses a liquid crystal display device which includes interleaved arrays of alternate parallel electrodes. A field is induced between interleaved electrodes.
Prior art optoceramic devices are disclosed in C. E. Land, P. D. Thatcher and G. H. Haertling, Electrooptic Ceramics, Academic Press, 1974 at pages 137-233.